Driving apparatus for lung ventilators



Oct.7, 1958 c. B. ANDREASEN 2,855,144

DRIVING APPARATUS FOR LUNG VENTILATORS Filed Nov. 7, 1955 2 Sheets-Sheet1 MICM 5r V /AM 4. Q -z Oct. 7, 1958 C. B. ANDREASEN DRIVING APPARATUSFOR LUNG VENTILATORS Filed Nov. '7, 1955 2 Sheets-Sheet 2 ATTORNEY 72,855,144 DRIVING APPARATUS FOR LUNG YENTILATORS Christian B. Andreasen,Elkins Park, Pa, assignor to Air- Shrelds, Inc.,.Bucks County, Pa., acorporation of Delaware 7 Application November 7, 1955, Serial No.545,192

Claims. (CL. 230 -162) This invention relates to lung ventilatingapparatus and is particularly concerned with improvements in the driving mechanism therefor.

Lung ventilators of the type to which the present improvements apply areespecially valuable when used with anesthesia machines. The ventilatorconstruction to which the present invention applies produces both apositive pressure phase and a negative pressure phase in the operatingcycle. The energy required during the positive phase is usuallydiiierent from the energy used during the negative phase.

As a result of this difference in phase energy require ments, when afree piston device is used to operate the apparatus, a longer pistontravel is normally needed in the direction requiring, the greater powerabsorption. Since the return stroke of the piston absorbs less energythe piston will travel only part of the way back. As a result afterseveral: strokes the piston will be operating near one end of thecylinder and there will be insutficient distance to give the length ofstroke needed to handle the higher energy phase.

The primary object of the present invention is the provision of simpleand effective means for solving this problem of shift in the operatingposition of the piston. To accomplish the desired results the presentinvention provides pressure relief devices which serve to allowrelatively free movement of the piston at the start of the stroke ineach direction. The eifective power for each phase is then developed inthe second portion of each stroke. In this manner the piston is alwaysin position to maintain the required movement to produce the pressuredesired for an adequate interval.

Another object of the invention is to provide an irnproved timing andcontrol system for producing the positive and negative phases in thepressure chamber of the ventilating device. relief valves in thepressure chamber for controlling the lung pressures and provides propercontrol through pressure regulators which supply the gas for the doubleacting driving piston. With this system, when a bellows is used as thevariable pressure chamber, there is definite relationship between thestroke of the bellows and the amount of gas which reaches the patient.Thus there is an indication of the amount of ventilation being provided.

How these and other more specific objects and advantages of theinvention are attained will be clear from the following description ofthe drawings, in which Figure 1 is an elevation view with certain partsin section showing the driving piston and variable pressure chamber of aventilating system.

Figure 2 is a sectional elevation of the driving portion showing thepiston at the lower end of its stroke.

Figure 3 is a sectional view similar to Figure 2 showing the piston atthe upper end of its stroke.

Figure 4 shows a sectional view of another form of piston drive with thevariable pressure chamber together with a schematic arrangementshowing'the supply system for the actuating gas.

The improved system eliminates the 27,855,144 Patented Oct. 7, 1958Figure 5 is a sectional elevation of the moving parts of the drivesystem of Figure 5 showing the piston at the lower end of the stroke.

Figure 6 is a view similar to Figure 5 with the piston at the upper endof the stroke. 7

In Figure 1 there'is illustrated a variable pressure chamber 11 to whichit attached a bellows unit 12, the actuation of which produces thevariations in pressure in the chamber 11. Relief valve unit 13 controlsthe degree of positive pressure in chamber 11 and relief valve unit 14controls the value of the negative pressure in the chamber. Breathingbag 15 is connected by duct 16 with the lungs of the patient through theanesthesia machine system. Chamber 1 1 is preferably transparent so thatthe action of bag 15 may be observed. A

Bellowsll is actuated by piston rod 17 which is connected to piston 18supported, in cylinder 19. At the lower end of the cylinder, tube 20 isconnected to deliver air for operating the piston. Timing mechanism notshown) is usedto control air delivered through 20'which moves the pistonin the upwardly direction for the positive pressure portion-of thecycle. For the downward or negative stroke of the piston the air supplyis closed ofi by the timing mechanism and the tube 20 is connected toatmospheric pressure. The downward stroke of the pi'ston'occurs due tothe weight ofthe piston 18 and the weight 21 attached'to the lower endof the b'el lows unit. Weight 21 is capable of producing the desirednegative pressure in chamber 11'. The air supply portion of the systemmentioned above may be similar to that shown in my co-pendingapplication 485,229; filed January 31, .1955. i

In the form of apparatus shown in Figures 1, 2, and 3 the mechanismwhich provides for proper utilization of the piston stroke is located atthe upperend of the cylinder where it supports pistonrod-17. The upperend of cylinder 19- is provided withthickened portion 22 which in turnsupports an upwardly extending tubular member 23 surroundingpiston rod17. Seals 24 and 24a are provided at the upper and lower ends of thepiston supporting structure; Theinside of tubular member 23 is larger indiameter than piston rod- 17 thereby'providing an annular space 25surrounding the piston rodbetween upper seal 24 and lower seal 24a. Inthe upper portion 22 of cylinder 19 various valve and channel structuresare incorporated. An adjustable valve26 having tapered portion 27extends into horizontal bore 28. Channel 29 extends from the inside ofthe cylinder to bore 28 and another channel 30 extends from the outerend of bore 28' to the outside air. Thus by adjusting valve 26 in wardlyor outwardly theflow through channel 28 may be restricted to give thedesired resistance.

A channel 31 connects into annular space 25 and extendsthrough thickenedportion 22' of the cylinder to connect with certain check valves. A ballcheck valve 32 is shown mounted between channel- 31- and the outside airwhile flap check valve 33 controls flow betweenchannel; 31 and the-upperend of cylinder 19" above piston-18.

A longitudinal slot 34 is providedinpist'onrod17. The length of slot 34and' the distance between seals 24 and 24a are so related to thestrokeof piston that thedesired load released over a portion of eachpistonstroke is provided.

In Figure 2 piston 18" is shown at thebottom' of'the stroke ready tomove upwardly through the positive phase ofthe' cycle. During theportion of the stroke" from piston position 18a t'ojdott'ed line pistonposition 1812', slo t 34' bypasses seal 2422 and connects the interioro'f the cylinder above the piston 18 to annular spa'ce25. Thus releaseof air is permitted from the upper portionof the cylinder through reliefvalve 32. In this way no appreciable resistance to the motion of thepiston is developed by compression effect above the piston. Howeverafter the pistonreaches position 18b, the lower end of slot 34 is abovelower seal 24a so that there is no open channel between the cylinder andannular space 25. Flapper valve 33 remains closed due to pressuredeveloped in the cylinder. The only release channel for the remainder ofthe up stroke is through restricted channel 29, 28, 30. Thus aresistance is developed during the last part of the stroke from position18b to the top end of the cylinder, position 180 in Figure 3. Duringthis second portion of the upward stroke the speed of piston travel isreduced. 7

Throughout this upward or pressure stroke the pressure in chamber 11remains at the value permitted by the setting of positive pressurerelief valve 13. During the first portion of the upward strokeconsiderable excess air is passed through relief valve 13. During theportion of the stroke between position 18b and 180 the reduced velocityof the piston reduces the flow through valve 13. However sufiieientdisplacement occurs to maintain pressure on bag 15 to provide thecollapsing action throughout the complete positive pressure interval asdetermined by the timing mechanism.

The downward stroke giving the negative portion of the cycle iscontrolled in generally similar fashion to that for the positivepressure portion of the cycle. Referring to Figure 3, as piston 18 movesfrom top position 180 downwardly toward position 18d a negative pressureis induced in the chamber 11. The magnitude of the negative pressure iscontrolled by relief valve 14 which admits outside air to chamber 11when the value of the negative pressure reaches the setting of reliefvalve 14. During the first part of the downward stroke of piston 18 airis admitted from the outside atmosphere through groove or channel 34past the seal 24 to the small fixed volume chamber formed by annularspace 25 and thence through channel 31 and-flapper relief valve 33(position 33a) which admits air to the upper portion of the cylinderabove the piston. Thus during the portion of piston travel from 18cposition to 18d position the motion is relatively fast because of thefree flow of the air into the upper portion of the cylinder. It shouldbe noted that during this portion of the stroke tube 20 is relieved toatmospheric pressure by the timing mechanism so that there is noresisting pressure in the lower portion of the cylinder 19 below thepiston.' Thus there is no compression effect which would reduce thevelocity of the piston motion. 7

When the piston reaches position 18d the upper end of slot or channel 34(see position 34d) has reached upper seal 24. As soon as the end of slot34 passes inside seal 24 air can no longer be admitted from the outsideto annular chamber 25. As a result there is no further free flow fromthe atmosphere to the part of the cylinder above the piston. The 'onlypassagefor airflow to the cylinder is through restricted channel 30, 28,29. Thus for the remainder of the stroke from 18d to the bottom positionof thsfpiston the rate of travel is materially reduced because of therestraining effect of the negative pressure above the piston induced bythe restricting action of the'air flow through the channel 29. Duringthe complete downward stroke of the piston the negative pressure in thechamber 11 has been maintained at constant value by the action of reliefvalve 14. 7

With this valve arrangement the piston is always positioned to provide afully eifective stroke in either direction.- Thus the first part of thepositive pressure stroke from position 18a to position 18b occurs in ashort period; of time. :The restricted portion of the positive pressurestroke from position 18b to top position 180 requires a much longerperiod of time.'- Therefore the piston will always be above position 18bbefore the timing device calls for the negative phase of the cycle.Likewise during the negative phase the piston travels from 180 to 18d ina very short interval while its travel from position 18d to the bottomof the stroke occurs in a relatively longer interval. Thus the majorportion of the negative cycle occurs during the last part of thedownward stroke. The piston will always be lower than position 18dbefore the timing device calls for the positive pressure phase of thecycle. In this way the piston is always re-positioned to give anadequate positive pressure stroke even though the negative phase of thecycle may be of shorter duration than the positive phase. Thus thestroke from 18d to 180 is always available for the positive pressurephase even though this full distance is not usually needed. Also thestroke from 18b to 18a is always available for the negative phase eventhough only a portion of this is normally used.

Figures 4, 5 and 6 shows a somewhat different form of operatingmechanism for producing the stroke utilization action. In Figure 4 thecontrol system for the driving air is shown in diagrammatic form. Itwill be seen that piston 35 which operates in cylinder 36 isdouble-acting. In this form of the apparatus there are no relief valvesassociated with chamber 37. Thus the positive pressure in variablepressure chamber 37 is determined directly by the pressure applied tothe piston 35 on the up-stroke. The positive pressure is applied bymeans of air delivered to the lower part of cylinder 36 through line 38.During the up-stroke of piston 35 the bellows 39 is collapsing anddeveloping the positive pressure in chamber 37 thus giving the positivepressure phase of the cycle. Similarly the negative pressure phase ofthe cycle is developed during the down-stroke of piston 35 and thepressure value in chamber 37 is determined by the degree of pressureapplied to the upper side of piston 35. A switching valve unit 40controls the application of pressure to the lower side and the upperside of piston 35 and determines the timing for each phase. Switchingvalve 40 incorporates valve 41 for controlling the air supply to thelower end of the cylinder and valve 42 for controlling the air supply tothe upper end of the cylinder. A hollow rod 43 which is attached to thediaphragm 44 controls the opening and closing of valves 41 and 42.Chamber 45 connects with the lower end of cylinder 36 through line 38and chamber 46 connects with the upper end of cyinder 36 through line47. A closed chamber 48 is provided on the lower side of diaphragm 44and atmospheric pressure chamber 49 is provided above diaphragm 44.Openings 50 lead from chamber 49 to the atmosphere. Also an opening 51in hollow rod or tube 43 provides for flow of air from the inside oftube 43 to atmosphere. Seals 53 prevent leakage from chambers 45 or 46around rod 43.

Air is supplied to the system through line 54. Regulator 55 controls theflow of air through timer 56 which in turn controls the air through line57 to chamber 48. Another regulator 58 controls the How of air to line59 leading to valve 41. Similarly regulator 60 controls the flow of airthrough line 61 leading to upper valve 42 of the switching valve unit40.

Timing device 56 is constructed to admit air under pressure from theregulator 55 to the diaphragm chamber 48 at predetermined intervals fora predetermined time after which it releases the pressure from chamber48 for a predetermined interval before repeating the cycle. By means ofadjustments in the timing device the length of the pressure appliedperiod and the pressure released period may be varied to provide thedesired time for the positive phase and the negative phase of theoperating cycle. With the timer in position so that the pressure inchamber 48 is released, diaphragm 44 will be forced downwardly by spring52 so that the end of tube 43 pushes against valve 41 to hold it in theopen position. While holding valve 41 it will be noted that the end oftube 43 against valve 41 is sealed. However in this posi-.

tion the upper end of tube 43 is removed from upper valve 42 and thusvalve 42 closes and the upper end of tube 43 opens into upper chamber46. With this setting the air in pipe 59 can flow through valve 41 intochamber 45 and through line 33 to the lower side of piston 35 to developpressure in the lower portion of the cylinder. During the time pressureis being transmitted through valve 41 air may flow from the upperportion of cylinder 36 through line 47 to chamber 46 and through theinside of tube 43 out through opening 51 to the atmosphere. Thus Whilepressure is being developed under piston 35 the trapped air at the upperside of piston 35 is released to the atmosphere.

This condition continues until the timer operates to supply air underpressure to chamber 48 and move diaphragrn 44 to its upper positionagainst the action of spring 52. The diaphragm then carries tube 43upwardly so that it permits the valve 41 to close and causes the valve42 to open. At the same time the upper end of tube 43 is closed and thelower end is opened to connect with chamber 45. Under this condition theflow is such that air under pressure is supplied through valve 42,chamber 46 and line 47 to the upper side of piston 35 and causes piston35 to move downwardly. At the same time cylinder 36 under the piston 35relieves to the atmosphere through line 38, chamber 45 and through tube43 with its opening 51. This condition continues until the timer againmoves to cut oif the supply of air to chamber 46 and relieve it toatmospheric to permit the diaphragm to shift the position of tube 43again.

The timing action may be changed by adjusting regulator 55. The pressureapplied to the lower side of piston 35 during the positive phase actionmay be regulated by adjusting regulator 53 thus controlling themagnitude of the pressure developed in chamber 37 during the positivephase. Likewise the negative pressure developed in chamber 37 isregulated by adjusting regulator 60 to control the negative phase actionof the device.

In this construction as in the previously described con struction ofFigures 1, 2 and 3, the free piston 35 operates bellows 39 by means of apiston rod which is in the form of tube 62. Thus if one phase of thecycle is longer in duration than the other, there is a tendency for thepiston to change its neutral position and gradually the stroke will betoward the end of the piston having the shorter duration. The effectiveworking action of the piston will become insufficient for developing thecomplete phase. To prevent this, relief valve mechanism is provided torelieve the pressure in the bellows during a portion of each stroke.

Piston tube 62 is connected to the lower surface 63 of the bellows 39.At the bottom of chamber 37 is a diaphragm 64 having openings 65 to thebellows. Downwardly projecting rod 66 is connected to the diaphragm 64and extends into the inside of piston tube 62. Seals 67 and 68 areprovided in piston tube 62 at suitably spaced intervals. These sealsengage rod 66 and provide a fixed volume chamber in the form of annularspace 69 between rod 66 and piston tube 62. In the upper end of tube 62enlarged portion 70 supports a pair of relief valves. Relief valve 71permits flow from annular space 69 through channel 72 to the inside ofthe bellows 39. Flapper valve 73 permits flow from annular space 69through channel 72 outwardly through the valve to the atmosphere. Thuspositive pressure in bellows chamber 39 closes valve 71 while positivepressure in channel 72 causes opening of valve 73. An elongated slot 74is provided in rod 66 which is positioned with respect to the seals 67and 68 to give the desired relief action for piston 35 during. a portionof the travel of each stroke. It should further be noted that openings75 in piston tube 62 provide access to atmospheric pressure from theinside of piston tube 62 below seal 68.

In Figure 5 the piston is shown in position 35a at the bottom of thestroke ready to startthe pressure phase of the cycle. As the piston 35moves upwardly from position 3511 under the influence of pressureapplied to the lower end of the cylinder, bellows 39 proceeds tocollapse and air flows through slot 74 from bellows chamber 39 past seal67 to annular space 69 and thence through channel 72 and relief valve 73to atmospheric. Thus during the portion of the stroke from pistonposition 35a to piston position 35b there is little or no resistancedeveloped in the bellows chamber and as a result piston moves veryquickly from one position to the other. However as soon as the pistonreaches position 35b upper seal 67 has reached position 67b where it isat the top of slot 74. At this position air can no longer flow frombellows chamber 39 into slot 74 and since valve 71 is closed due to thepressure in' chamber 39 the pressure therefore immediately develops tothe amount determined by the pressure applied to the lower end ofcylinder 36. The portion of the stroke from position 35b upwardly to thetop of the piston stroke at 35c (Figure 6) is therefore the effectiveportion of the pressure stroke. During this time the desired positivepressure is developed in bellows chamber 39' and chamber 37 whichcontains the breathing bag. During this portion of the stroke, piston 35travels relatively slowly. The time of application of pressure iscontrolled by the switching valve. The travel above position 35b isgoverned by the volume of air delivered to the patients lungs.

For the down stroke, that is, the negative pressure phase of the cycle,pressure is applied to the cylinder above piston 35 beginning at its topposition 35c-see Figure 6. At this position any downward movement ofbellows 39 causes opening of valve 71 so that air at atmosphericpressure is admitted, travelling through opening 75 and slot 74 toannular space 69 and then through channel 72 and valve 71 into thebellows chamber 39. Thus during the first part of the downward stroke,since no negative pressure can be developed in the bellows 39, piston 35moves very rapidly from position 350 to position 35d.

When the piston has reached the position 35d lower seal 68 has reachedposition 68d at bottom end of slot 74 and as a result no further air canpass from the outside atmosphere through slot 74 into the bellowschamber. The bellows chamber is therefore effectively sealed andimmediately the negative pressure determined by ,the pressure applied topiston 35 is developed in the bellows chamber and chamber 37. Thedevelopment of this negative pressure immediately causes slowing down ofthe movement of piston 35 so that the remainder of the stroke fromposition 35d to the bottom end is at a greatly reduced rate andencompasses the major portion of the time required for the negativephase of the cycle. The volume of air withdrawn from the lungsdetermines the piston travel below 35d.

With this arrangement of valves to control the piston action, the mainworking portion of each piston stroke is toward the end of the stroke.Thus regardless of how much or how little of the working stroke isactually used during the effective portion of any piston action, thepiston is always in position to provide full effectiveness for the nextactive stroke in the reverse direction.

From the foregoing it will be seen that I have provided suitable valvestructure for assuring full effectiveness of every stroke of the freepiston whether or not the lengths of the phase cycles are equal. By theuse of the neutral chamber between the seals and the cooperative slottedchannel a simple mechanism is provided for producing rapid travel duringthe initial portion of the stroke in either direction of travel. By thismeans proper repositioning of the piston is assured so that no faultyfunctioning can be experienced because of displacement of the neutralposition of the stroke. With apparatus of the type disclosed it is alsopossible to combine etfective,

cycling control both as to adjustable timing of phases and as toeffective pressure control for both positive and negative phases. Withthe second form of equipment shown in which the bellows chamber issealed during the effective portions of both the positive phase and thenegative phase action, an indication of the amount of ventilation beingprovided to the lungs during anesthesia is provided. This indication isgiven by the position to which the bellows travels upwardly during thepositive phase and the position to which it travels downwardly duringthe negative phase. This relationship indicates therefore the amount ofgas which reaches a patient and provides a ready meansof checking theaction of the anesthesia machine.

I claim:

1. For lung ventilator apparatus and the like having two cycle phaseswherein one phase may have different duration and energy requirementsthan the other phase, actuating mechanism having a cylinder and pistonforming a variable volume chamber, a second variable volume chamberhaving a movable wall, a driving connection between said variable volumechambers, a fixed volume chamber, channel structure leading from saidfixed volume chamber to one of said variable volume chambers and to theoutside atmosphere, control means to close off the portion of saidchannel structure to said last mentioned one of said variable volumechambers during a predetermined portion of the stroke of said piston anda check valve in the portion of said channel structure to the outsideatmosphere.

2. Driving mechanism for lung ventilator apparatus and the likeincluding a cylinder and piston forming a variable volume chamber, meansincluding a fixed wall and a movable wall forming a second variablevolume chamber, a rod member, a tubular member around a portion of saidrod member with an annular clearance space therebetween, one of saidmembers forming a connection between said piston and said movable wall,the other of said members being supported in fixed relationship thereto,said tubular member supporting a pair of spaced seals which engage saidrod member to form the ends of a fixed volume chamber produced by theannular space, channel structure extending from said clearance space tothe outside atmosphere including a check valve, additional channelstructure leading from said clearance space to one of said variablevolume chambers including a second check valve, a further channelstructure positioned to extend from said clearance space to one of saidvariable volume chambers during a portion of the stroke of said piston.

3. Driving mechanism for apparatus such as a lung ventilator having twocycle phases, one of which may have different duration and energyrequirements than the other, said mechanism incorporating a cylinder andpiston, a cylindrical rod member, a tubular member positioned aroundsaid rod member to form an annular clearance space therebetween, one ofsaid members being connected to said piston and the other of saidmembers being supported in fixed relationship with respect to thepiston-connected member, said tubular member supporting a pair of spacedseals which also engage said rod member, channel means extendinglongitudinally in said rod member to provide a connection from saidclearance space to one side of said seals during one portion of thepiston stroke and from said space to the otherside of said seals duringanother portion of the stroke.

4. Actuating mechanism for lung ventilating apparatus and the likeincluding a cylinder and piston forming a variable volume chamber, abellows device forming a second variable volume chamber, a rod memberextending between said piston and said bellowsdevice, a neutral chamberlocated intermediate said variable volume chambers, channel and valvemeans .between said neutral chamber andone of said variable. volumechambers, channel and valve means between said neutral chamber and theoutside atmosphere, an air supply system for driving said piston in saidcylinder, an air supply switching valve in said system, an air lineextending from said switching valve to each end of said cylinder, saidswitchig valve incorporating a check valve device at each end thereof,one of said check valve devices controlling the fiow of air to one endof aid piston and the other of said check valve devices controlling theHow of air to the other end of said cylinder, a tubular member extendingbetween said check valve devices, a diaphragm attached to said tubularmember, a chamber in said switching valve having one of its walls formedby said diaphragm, an air line leading to said last mentioned chamber tosupply pressure for periodically shifting said tubular member foralternately opening one or the other of said check valve devices.

5. Actuating mechanism for lung ventilating apparatus and the likeincluding a cylinder and piston forming a variable volume chamber, abellows device forming a second variable volume chamber, a tubularpiston rod member extending between said piston and said bellows device,an elongated rod fixed to a wall of said bellows device and extendinginto said tubular piston rod member, said elongated rod being of smallerdiameter than the inside of said tubular piston rod member to form aclearance space therebetween, a pair of seals mounted in spacedrelationship in said tubular piston rod member and engaging the surfaceof said elongated rod, said elongated rod having a longitudinal channeltherein, channel and check valve means permitting flow from the annularspace between said seals to the bellows chamber and from the annularspace to the outside atmosphere, said check valve means preventing floweither from the bellows chamber or from the outside atmosphere into saidannular chamber.

6. Driving mechanism in accordance with claim 3 in which another channelmeans connects said clearance space with the outside atmosphere, atcheck valve to control flow to the outside atmosphere through said otherchannel means.

7. Driving mechanism for a lung ventilator or the like, said ventilatorhaving two cycles phases, one of said phases having different durationand energy requirements than the other, said mechanism incorporating acylinder and piston, a piston rod extending from said piston through oneend of said cylinder, piston rod supporting structure at the end of saidcylinder having clearance space between it and said rod, a pair of sealsmounted in spaced relationship in said supporting structure and engagingsaid rod, channel and valve means connected to said clearance space,said rod having a channel extending longitudinally along it, a bleedchannel structure extending from the inside of the piston rod end of thecylinder to the outside atmosphere, said bleed channel structureincorporating a valve to adjust the bleed rate.

8. Driving mechanism for a lung ventilator or the like, said ventilatorhaving two cycle phases, one of said phases having different durationand energy requirements than the other, said mechanism incorporating acylinder and piston, a piston rod extending from said piston through oneend of said cylinder, piston rod supporting structure at the end of saidcylinder having clearance space between it and said rod, a pair of sealsmounted in spaced relationship in said supporting structure and engagingsaid rod, said rod having a channel extending longitudinally along it,another channel to the end of said cylinder connected to said clearancespace and a third channel to theoutside atmosphere connected to saidclearance space, both the secondand third channels incorporating valvemeans to control the flow of gas therethrough.

9. Driving mechanism for a lung ventilator or the like, said ventilatorhaving two cycle phases, one of said phases having different durationand energy requirements than the other, said mechanism incorporating acylinder and piston, a piston rod extending from said piston through oneend of said cylinder, piston rod supporting structure at the end of saidcylinder having clearance space between said supporting structure andsaid piston rod, 21 pair of seals mounted in spaced relationship, achannel structure leading from said clearance space to the inside of thecylinder, 21 check valve in said channel structure to control the flowof gas between said clearance space and said cylinder.

10. Driving mechanism for a lung ventilator or the like, said ventilatorhaving two cycle phases, one of said phases having different durationand energy requirements than the other, said mechanism incorporating acylinder and piston, a piston rod extending from said piston through oneend of said cylinder, piston rod supporting References Cited in the fileof this patent UNITED STATES PATENTS Harter Nov. 4, 1941 Collins et a1.Feb. 11, 1947

